Dehydrogenation method and catalytic composite for use therein

ABSTRACT

DEHYDROGENATABLE HYDROCARBONS ARE DEHYDROGENATED BY CONTACTING SAME AT DEHYDROGENATION CONDITIONS WITH A CATALYTIC COMPOSITE, COMPRISING A COMBINATION OF CATALYTICALLY EFFECTIVE AMOUNTS OF A PLATINUM GROUP COMPONENT, A RHENIUM COMPONENT, AND A TIN COMPONENT WITH A POROUS CARRIER MATERIAL. A SPECIFIC EXAMPLE OF THE CATALYTIC COMPOSITES DISCLOSED HEREIN IS A COMBINATION OF A PLATINUM COMPONENT, A RHENIUM COMPONENT, A TIN COMPONENT, AND AN ALKALI OR ALKALINE EARTH COMPONENT WITH AN ALUMINA CARRIER MATERIAL WHEREIN THE COMPONENTS ARE PRESENT IN AMOUNTS SUFFICIENT TO RESULT IN THE CATALYTIC COMPOSITE CONTAINING, ON AN ELEMENTAL BASIS, 0.01 TO 1 WT. PERCENT PLATINUM, 0.01 TO 1 WT. PERCENT RHENIUM, 0.01 TO 5 WT. PERCENT TIN, AND 0.01 TO 5 WT. PERCENT OF THE ALKALI OR ALKALINE EARTH METAL.

United States Patent Ofice 3,576,766 Patented Apr. 27, 1971 U.S. Cl. 252--439 6 Claims ABSTRACT OF THE DISCLOSURE 'Dehydrogenatable hydrocarbons are dehydrogenated by contacting same at dehydrogenation conditions with a catalytic composite, comprising a combination of cata lytically effective amounts of a platinum group component, a rhenium component, and a tin component with a porous carrier material. A specific example of the catalytic composites disclosed herein is a combination of a platinum component, a rhenium component, a tin component, and an alkali or alkaline earth component with an alumina carrier material wherein the components are present in amounts sufficient to result in the catalytic composite containing, on an elemental basis, 0.01 to 1 wt. percent platinum, 0.01 to 1 wt. percent rhenium, 0.0l to wt. percent tin, and 0.01 to 5 wt. percent of the alkali or alkaline earth metal.

CROSS REF'ERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of my application entitled Hydrocarbon Conversion Process and Catalyst T herefor, Ser. No. 819,114, filed Apr. 24, 1969.

DISCLOSURE The subject of the present invention is, broadly, an improved method for dehydrogenating a dehydrogenatable hydrocarbon to produce a hydrocarbon product containing the same number of carbon atoms but fewer hydrogen atoms. In another aspect, the present invention encompasses a method of dehydrogenating normal paraffin hydrocarbons containing 4 to 30 carbon atoms per molecule to the corresponding normal mono-olefin with minimum production of side products. In yet another aspect, the present invention relates to a novel catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a rhenium component, a tin component, and an alkali or alkaline earth component with a porous carrier material, which catalytic composite has highly preferred characteristics of activity, selectivity, and stability when it is employed in the dehydrogenation of dehydrogenatable hydrocarbons such as aliphatic hydrocarbons, naphthene hydrocarbons, and alkylaromatic hydrocarbons.

The conception of the present invention followed from my search for a novel catalytic composite possessing hydrogenation-dehydrogenation and cracking functions and having superior conversion, selectivity, and stability characteristics when employed in hydrocarbon conversion processes that have traditionally utilized dual-function catalytic composites. In my prior application I disclosed a significant finding. with respect to a catalytic composite meeting these requirements. More specifically, I determined that a catalytic composite comprising a combination of a platinum group component, a rhenium component, and a tin component with a porous carrier material has superior activity, selectivity, and stability characteristics when it is employed in a process which heretofore utilized dual-function catalytic composites such as a dehydrogenation process. After an extensive investigation of the use of this composite in a dehydrogenation reaction, I have now determined that a particularly preferred catalytic composite for dehydrogenation contains not only a platinum group component, a rhenium component, and a tin component, but also an alkali or alkaline earth component.

The dehydrogenation of dehydrogenatable hydrocarbons is an important commercial process because of the great and expanding demand for dehydrogenated hydrocarbons for use in the manufacture of various chemical products such as detergents, plastics, synthetic rubbers, pharmaceutical products, high octane gasoline, perfumes, drying oils, ion-exchange resins, and various other products well known to those skilled in the art. One example of this demand is in the manufacture of high octane gasoline by using C and C mono-olefins to alkylate isobutane. Another example of this demand is in the area of dehydrogenation of normal parafiin hydrocarbons to produce normal mono-olefins having 4 to 30 carbon atoms per molecule. These normal mono-olefins can, in turn, be utilized in the synthesis of vast numbers of other chemical products. For example, derivatives of normal mono-olefins have become of substantial importance to the detergent industry where they are utilized to alkylate an alkylatable aromatic, such as benzene, with resultant transformation of the product arylalkane into a wide variety of biodegradable detergents such as the alkylaryl sulfonate type of detergent which is most widely used today for household, industrial, and commercial processes. Still another large class of detergents produced from these normal mono-olefins are the oxyalkylated phenol derivatives in which the alkyl phenol base is prepared by the alkylation of phenol with these normal mono-olefins. Still another type of detergents produced from these normal mono-olefins are the biodegradable alkylsulfates formed by the direct sulfation of the normal mono-olefin. Likewise, the olefin can be subjected to direct sulfonation with sodium bisulfite to make biodegradable alkylsulfonates. As a further example, these mono-olefins can be hydrated to produce alcohols which then, in turn, can be used to produce plasticizers and/or synthtic lube oils.

Regarding the use of products made by the dehydrogenation of alkylaromatic hydrocarbons, these find wide application in industries including the petroleum, petro chemical, pharmaceutical, detergent, plastic industries, and the like. For example, ethylbenzene is dehydrogenated to produce styrene which is utilized in the manufacture of polystyrene plastics, styrene-butadiene rubber, and the like products. Isopropylbenzene is dehydrogenated to form alphamethyl styrene which, in turn, is extensively used in polymer formation and in the manufacture of drying oils, ion exchange resins, and the like material.

Responsive to this demand for these dehydrogenation products, the art has developed a number of alternative methods to produce them in commercial quantities. One method that is widely utilized involves the selective dehydrogenation of dehydrogenatable hydrocarbon by contact ing the hydrocarbon with a suitable catalyst at dehydrogenation conditions. As is the case with most catalytic procedures, the principal measure of effectiveness for this dehydrogenation method involves the ability to perform its intended function with minimum interference of side reactions for extended periods of time. The analytical terms used in the art to broadly measure how well a particular catalyst performs its intended functions in a particular hydrocarbon conversion reaction are activity, selectivity, and stability, and for purposes of discussion here these terms are generally defined for a given reactant as follows: (1) activity is a measure of the catalysts ability to convert the hydrocarbon reactant into products at a specified severity level where severity level means the conditions usedthat is, the temperature, pressure, contact time, and presence of diluents such as H (2) selectivity usually refers to the amount of desired product or products obtained relative to the amount of the reactant converted; (3) stability refers to the rate of change with time of the activity and selectivity parameters-obviously the smaller rate implying the more stable catalyst. More specifically, in a dehydrogenation process, activity commonly refers to the amount of conversion that takes place for a given dehydrogenatable hydrocarbon at a specified severity level and is typically measured on the basis of disappearance of the dehydrogenatable hydrocarbon; selectivity is typically measured by the amount, calculated on a mole percent of converted dehydrogenatable hydrocarbon basis, of the desired dehydrogenated hydrocarbon obtained at the particular severity level; and stability is typically equated to the rate of change with time of activity as measured by disappearance of the dehydrogenatable hydrocarbon and of selectivity as measured by the amount of desired hydrocarbon produced. Accordingly, the major problem facing workers in the hydrocarbon dehydrogenation art is the development of a more active and selective catalytic composite that has good stability characteristics.

I have now found a catalytic composite which possesses improved activity, selectivity, and stability when it is employed in a process for the dehydrogenation of dehydrogenatable hydrocarbons. In particular, I have determined that a combination of catalytically effective amounts of a platinum group component, a rhenium component, and a tin component with a porous, refractory carrier material enables the performance of a dehydrogenation process to be substantially improved. Moreover, I have observed particularly good results when this composite is combined with an alkali or alkaline earth component and utilized to produce dehydrogenated hydrocarbons containing the same carbon structure as the reactant hydrocarbon but fewer hydrogen atoms. This last composite is particularly useful in the dehydrogenation of long chain normal parafiins to produce the corresponding normal mono-olefin with minimization of side reactions such as skeletal isomerization, aromatization, and cracking.

It is, accordingly, one object of the present invention to provide a novel method for the dehydrogenation of dehydrogenatable hydrocarbons utilizing a catalytic composite comprising a platinum group component, a rhenium component, and a tin component combined with a porous carrier material. A second object is to provide a novel catalytic composite having superior performance characteristics when utilized in a dehydrogenation process. Another object is to provide an improved method for the dehydrogenation of normal paraffin hydrocarbons to produce normal mono-olefins which method minimizes undesirable side reactions such as cracking, skeletal isomerization, and aromatization.

In brief summary, one embodiment of the present invention involves a method for dehydrogenating a dehydrogenatable hydrocarbon which comprises contacting the hydrocarbon with a catalytic composite containing a platinum group component, a rhenium component, and a tin component combined with a porous carrier material at dehydrogenation conditions. The catalytic composite contains these components in an amount, calculated on an elemental basis, of about 0.01 to about 1 wt. percent platinum group metal, about 0.01 to about 1.0 wt. percent rhenium, and about 0.01 to about 5 wt. percent tin.

A second embodiment relates to the dehydrogenation method described in the first embodiment wherein the dehydrogenatable hydrocarbon is an aliphatic compound containing 2 to 30 carbon atoms per molecule.

A third embodiment relates to a catalytic composite comprising a combination of a platinum group component, a rhenium component, a tin component, and an alkali or alkaline earth component with an alumina carrier material. These components are present in amounts 4 sufficient to result in the catalytic composite containing, on an elemental basis, about 0.01 to about 1 wt. percent platinum group metal, about 0.01 to about 1.0 wt. percent rhenium, about 0.01 to about 5 wt. percent tin, about 0.01 to about 5 wt. percent of the alkali metal or alkaline earth metal.

Another embodiment relates to a method for dehydrogenating a dehydrogenatable hydrocarbon which comprises contacting the hydrocarbon with the catalytic composite described in the third embodiment at dehydrogenation conditions.

Other objects and embodiments of the present invention concern specific details regarding essential and preferred catalytic ingredients, preferred concentration of components in the composite, suitable methods of composite preparation, suitable dehydrogenatable hydrocarbons, operating conditions for use in the dehydrogenation process, and the like particulars. These are hereinafter given in the following detailed discussion of each of these facets of the present invention.

Regarding the dehydrogenatable hydrocarbon that is subjected to the method of the present invention, it can, in general, be an organic compound having 2 to 30 carbon atoms per molecule and containing at least 1 pair of adjacent carbon atoms having hydrogen attached thereto. That is to say, it is intended to include within the scope of the present invention, the dehydrogenation of any organic compound capable of being dehydrogenated to produce products containing the same number of carbon atoms but fewer hydrogen atoms, and capable of being vaporized at the dehydrogenation temperatures used herein. More particularly, suitable dehydrogenatable hy drocarbons are: aliphatic compounds containing 2 to 30 carbon atoms per molecule, alkylaromatic hydrocarbons Where the alkyl group contains 2 to 6 carbon atoms, and naphthenes or alkyl-substituted naphthenes. Specific examples of suitable dehydrogenatable hydrocarbons are: (l) alkanes such as ethanes, propane, n-butane, isobutanes, n-pentane, isopentanes, n-hexane, Z-methylhexane, and the like compounds; (2) naphthenes such as cyclopentane, cyclohexane, methylcyclopentane, 1,3-dimethyl-- cyclohexane, and the like compounds; and (3) alkylaromatics such as ethylbenzene, n-butylbenzene, 1,3,5-triethylbenzene, isopropylbenzene, ethylnaphthalene, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normal paraffin hydrocarbon having about 4 to about 30 carbon atoms per molecule. For example, normal paraffin hydrocarbons containing about 10 to 15 carbon atoms per molecule are dehydrogenated by the subject method to produce the corresponding normal mono-olefin which can, in turn, be alkylated with benzene and sulfonated to make alkylbenzene sulfonates detergents having superior biodegradability. Likewise, nalkanes having 12 to 18 carbon atoms can be dehydrogenated to the corresponding normal mono-olefin which, in turn, can be sulfated or sulfonated to make excellent detergents. Similarly, n-alkane having 6 to 10 carbon atoms can be dehydrogenated to form the corresponding mono-olefin which can, in turn, be hydrated to produce valuable alcohols. Preferred feed streams for the manufacture of detergent intermediates contains a mixture of 4 or 5 adjacent normal paraffin homologues such as C to C C to C C to C and the like mixtures.

An essential feature of the present invention involves the use of a catalytic composite comprising a combination of catalytically efiective amounts of a platinum group component, a rhenium component, and a tin component with a porous carrier material. In a preferred embodiment, this catalytic composite also contains an alkali or alkaline earth component.

Considering first the porous carrier material utilized in the present invention, it is preferred that the material be a porous, adsorptive, high-surface area support hav ing a surface area of about 25 to about 500 m. gm. The

porous carrier material should be relatively refractory to the conditions utilized in the hydrocarbon conversion process, and it is intended to include within the scope of the present invention carrier materials which have traditionally been utilized in dual-function hydrocarbon conversion catalysts such as: (l) activated carbon, coke, or charcoal; (2) silica or silica gel, silicon carbide, clays, and silicates including those synthetically prepared and naturally occurring, which may or may not be acid treated, for example, attapulgus clay, china clay, diatomaceous earth, fullers earth, kaolin, kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite; (4) refractory inorganic oxides such as alumina, titanium di oxide, zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria, silica-alumina, silica-magnesia, chromia-alumina, alumina-boria, silica-zirconia, etc.; (.5) crystalline aluminosilicates such as naturally occurring or synthetically prepared mordenite and/ or faujuasite, either in the hydrogen form or in a form which has been treated with multivalent cations; and (6) combination of these groups. The preferred porous carrier materials for use in the present invention are refractory inorganic oxides with best results obtained with an alumina carrier material. Suitable alumina materials are the crystalline aluminas known as the gamma-, eta-, and thetaalumina with gammaor eta-alumina giving best results. In addition, in some embodiments the alumina carrier material may contain minor proportions of other well known refractory inorganic oxides such as silica, zirconia, magnesia, etc.; however, the preferred support is substantially pure gammaor eta-alumina. Preferred carrier materials have an apparent bulk density of about 0.3 to about 0.7 gm./cc. and surface area characteristics such that the average pore diameter is about 20 to 3000 angstroms, the pore volume is about 0.1 to about 1 mL/mg. and the surface area is about 100 to about 500 m. gm. In general, best results are typically obtained with a gamma-alumina carrier material which is used in the form of spherical particles having: a relatively small diameter (i.e., typically about inch), an apparent bulk density of about 0.5 gm./cc., a pore volume of about 0.4 ml./gm., and a surface area of about 175 mF/gm.

The preferred alumina carrier material may be prepared in any suitable manner and may be synthetically prepared or natural occurring. Whatever type of alumina is employed it may be activated prior to use by one or more treatments including drying, calcination, steaming, etc., and it may be in a form known as activated alumina, activated alumina of commerce, porous alumina, alumina gel, etc. For example, the alumina carrier may be prepared by adding a suitable alkaline reagent, such as ammonium hydroxide to a salt of aluminum such as aluminum chloride, aluminum nitrate, etc., in an amount to form an aluminum hydroxide gel which upon drying and calcining is converted to alumina. The alumina carrier may be formed in any desired shape such as spheres, pills, cakes, extrudates, powders, granules, etc., and utilized in any desired size. For the purpose of the present invention a particularly preferred form of alumina is the sphere; and alumina spheres may be continuously manufactured by the well known oil drop method which comprises: forming an alumina hydrosol by any of the techniques taught in the art and preferably by reacting aluminum metal with hydrochloric acid, combining the resulting hydrosol with a suitable gelling agent and dropping the resultant mixture into an oil bath maintained at elevated temperatures. The droplets of the mixture remain in the oil bath until they set and form hydrogel spheres. The spheres are then continuously withdrawn from the oil bath and typically subjected to specific aging treatments in oil and an ammoniacal solution to further improve their physical characteristics. The resulting aged and gelled particles are then washed and dried at a relatively low temperature of about 300 F. to about 400 F. and subjected to a calcination procedure at a temperature of about 850 F. to about 1300 F. for a period of about 1 to about 20 hours. It is also a good practice to subject the calcined particles to a high temperature steam treatment in order to remove as much as possible of undesired acidic component. This manufacturing procedure effects conversion of the alumina hydrogel to the corresponding crystalline gamma-alumina. See the teachings of U.S. Pat. No. 2,620,314 for additional details.

One essential constituent of the catalyst of the present invention is a tin component. This component may be present as an elemental metal or as a chemical compound such as the oxide, sulfide, halide, etc., and may be utilized in any amount which is catalytically effective. Preferably, the tin component is used in an amount sufficient to result in the final catalytic composite containing, on an elemental basis, about 0.01 to about 5.0 wt. percent tin, with best results typically obtained with about 0.1 to about 1.0 wt. percent tin. This component may be incorporated in the catalytic composite in any suitable manner such as by coprecipitation or cogellation with the porous carrier material, ion exchange with the carrier material or impregnation of the carrier material at any stage in the preparation. It is to be noted that it is intended to include within the scope of the present invention all conventional methods for incorporating a metallic component in a catalytic composite, and the particular method of incorporation used is not deemed. to be an essential feature of the present invention. One preferred method of incorporating the tin component into the catalytic composite involves coprecipitating the tin component during the prep aration of the preferred refractory oxide carrier material. In the preferred case, this involves the addition of suitable soluble, decomposable tin compounds such as stannous or stannic halide to the alumina hydrosol, and then combining the hydrosol with a suitable gelling agent and dropping the resulting mixture into an oil bath, etc., as explained in detail hereinbefore. Following the calcination step, there is obtained a carrier material comprising an intimate combination of alumina and stannic oxide. Another preferred method of incorporating the tin component into the catalyst composite involves the utilization of a soluble, decomposable compound of tin to impregnate the porous carrier material. Thus, the tin component may be added to the carrier material by commingling the latter with an aqueous solution of a suitable tin salt or water-soluble compound of tin such as stannous bromide, stannous chloride, stannic chloride, stannic chloride pentahydrate, stannic chloride tetrahydrate, stannic chloride trihydrate, stannic chloride diamino, stannic trichloride bromide, stannic chromate, stannous fluoride, stannic fluoride, stannic iodide, stannic sulfate, stannic tartrate, and the like compounds. The utilization of a tin chloride compound such as stannous or stannic chloride is particularly preferred since it facilitates the incorporation of both the tin component and at least a minor amount of the preferred halogen component in a single step. In general, the tin component can be impregnated either prior to, simultaneously with or after the other metallic components are added to the carrier material. However, I have found that excellent results are obtained when the tin component is impregnated simultaneously with the platinum and rhenium components. In fact, a me ferred impregnation solution contains chloroplatinic acid, perrhenic acid, nitric acid, and stannous or stannic chloride. Following the impregnation step, the resulting composite is typically dried and calcined or as is explained hereinafter.

Another essential component for the catalytic composite used in the present invention is a platinum group component. Although the process of the present invention is specifically directed to the use of a catalytic composite containing platinum, it is intended to include other platinum group metals, such as palladium, rhodium, ruthenium, osmium, and iridium. The platinum group metallic component such as platinum may exist Within the final catalytic composite as a compound such as an oxide, sulfide, halide, etc., or as an elemental metal. Generally, the amount of the platinum group metallic component present in the final catalyst is small compared to the quantities of the other components combined therewith. In fact, the platinum group metallic component generally comprises about 0.01 to about 1% by weight of the final catalytic composite calculated on an elemental basis. Excellent results are obtained when the catalyst contains about 0.1 to about 0.9 wt. percent of the platinum group metal. The preferred platinum group component is platinum or a compound of platinum.

'Ihe platinum group metallic component may be incorporated in the catalytic composite in any suitable manner such as coprecipitation or cogellation with the preferred alumina carrier material, ion exchange with the alumina carrier material and/or alumina hydrogel, or impregnation either after or before calcination of the alumina hydrogel, etc. The preferred method of preparing the catalyst involves the utilization of a soluble, decomposable compound of the platinum group metal to impregnate the porous carrier material. Thus, the platinum group metal may be added to the carrier by commingling the latter with an aqueous solution of chloroplatinic acid. Other water-soluble compounds of platinum may be employed as impregnation solutions and include ammonium chloroplatinate, platinum chloride, dinitrodiaminoplatinum, etc. The utilization of a platinum chloride compound such as chloroplatinic acid is ordinarily preferred. In addition, it is generally preferred to impregnate the carrier material after it has been calcined in order to minimize the risk of washing away the valuable platinum metal compounds; however, in some cases it may be advantageous to impregnate the carrier when it is in a gelled state. Following the impregnation step, the resulting impregnated support is dried and subjected to a high temperature calcination as explained hereinafter.

Yet another essential component of the catalyst used in the present invention is the rhenium component. This component may be present as an elemental metal, as a chemical compound such as the oxide, sulfide, halide, etc., or as a physical or chemical combination with the porous carrier material and/or other components of the catalytic composite. The rhenium component is preferably utilized in an amount sufficient to result in a final catalytic composite containing about 0.01 to about 1 wt. percent rhenium, calculated on an elemental basis. The rhenium component may be incorporated in the catalytic composite in any suitable manner and at any stage in the preparation of the catalyst. It is generally advisable to incorporate the rhenium component in an impregnation step after the porous carrier material has been formed in order that the expensive metal will not be lost due to washing and purification treatments which may be applied to the carrier material during the course of its production. Although any suitable method for incorporating a catalytic component in a porous carrier material can be utilized to incorporated the rhenium component, the preferred procedure involves impregnation of the porous carrier material. The impregnation solution can, in general, be a solution of a suitable soluble, decomposable rhenium salt such as ammonium perrhenate, sodium perrhenate, potassium perrhenate, and the like salts. In addition, solutions of rhenium halides such as rhenium chloride may be used; the preferred impregnation solution is, however, an aqueous solution of perrhenic acid. The porous carrier material can be impregnated with the rhenium component either prior to, simultaneously with, or after the other components mentioned herein are combined therewith. Best results are ordinarily achieved when the rhenium component is impregnated simultaneously with the platinum group component. In fact, excellent results have been obtained with a one-step impregnation procedure utilizing as an impregnation solution, an aqueous solution of chloroplatinic acid, perrhenic acid, stannic chloride,

and nitric acid.

Regarding the preferred amounts of the various metal- 11c components of the subject catalyst, I have found it to be a good practice to specific the amounts of the rhenium component and of the tin component as a function of theamount of the platinum group component. On this basls, the amount of the rhenium component is ordinarily selected so that the atomic ratio of the platinum group metal to rhenium contained in the composite is about 0.05:1 to about 2.75:1 with the preferred ra'nge being about 0.25:1 to about 2:1. Similarly, the amount of the tin component is ordinarily selected to produce a composite containing an atomic ratio of the platinum group metal to tin of about 0.1:1 to about 3:1 with the preferred range being about 0.5 :1 to about 1521.

Another significant parameter for the subject catalyst is the total metals content which is defined to be the sum of the platinum group component, the rhenium component, and the tin component, calculated on an elemental tin, rhenium, and the platinum group metal basis. Good results are ordinarily obtained with the subject catalyst when this parameter is fixed at a value of about 0.03 to about 3 wt. percent with best results ordinarily achieved at a metals loading of about 0.15 to about 2 wt. percent. Integrating the above discussion of each of the essential components of the catalytic composite used in the present invention, it is evident that a particularly preferred catalytic composite comprises a combination of a platinum component, a rhenium component, and a tin component with an alumina carrier material in amounts sufiicient to result in the composite containing about 0.01 to about 1 wt. percent platinum, about 0.01 to about 1 wt. percent rhenium, and about 0.01 to about 5 wt. percent tin. Accordingly, specific examples of especially preferred catalytic composites are as follows: (1) a catalytic composite comprising a combination of .5 wt. percent tin, .5 wt. percent rhenium, and .75 wt. percent platinum with an alumina carrier material; (2) a catalytic composite comprising a combination of .1 wt. percent tin, 0.1 wt. percent rhenium, and 0.1 wt. percent platinum with an alumina carrier material; (3) a catalytic composite comprising a combination of about .375 wt. percent tin, .37 5 wt. percent rhenium, and .375 wt. percent platinum with an alumina carrier material; (4) a catalytic composite comprising a combination of .12 wt. percent tin, .1 wt. percent rhenium, and .2 wt. percent platinum with an alumina carrier material; (5) a catalytic composite comprising a combination of 0.25 wt. percent tin, 0.25 wt. percent platinum, 0.25 wt. percent rhenium with an alumina carrier material; and (6) a catalytic com-posite comprising a com- ;bination of 0.2 wt. percent tin, 0.2 wt. percent rhenium, and 0.2 wt. percent platinum with an alumina carrier material. The amounts of the components reported in these examples are, of course, calculated on an elemental basis.

.As indicated above, a preferred embodiment of the present invention involves use of a catalytic composite containing an alkali or alkaline earth component. More specifically, this component is selected from the group consisting of the compounds of the alkali metals-cesium, rubidium, potassium, sodium, and lithium-and of the alkaline earth metals-calcium, strontium, barium, and magnesium. This component may exist within the catalytic composite as a relatively stable compound such as the oxide or sulfide, or in combination with one or more of the other components of the composite, or in combination with an alumina carrier material such as in the form of a metal aluminate. Since, composite containing the alkali or alkaline earth is always calcined in an air atmosphere before use in the conversion of hydrocarbons, the most likely state this component exists in during use in dehydrogenation is the metallic oxide. Regardless of what precise form in which it exists in the composite, the amount of this component utilized is preferably selected to provide a composite containing about 0.01 to about 5 wt. percent of the alkali or alkaline earth metal, and more preferably about 0.05 to about as is explained hereinafter, the

2.5 wt. percent. Best results are ordinarily achieved when this component is a compound of lithium or potassium.

This alkali or alkaline earth component may be combined with the porous carrier material in any manner known to those skilled in the art such as by impregnation, coprecipitation, physical admixture, ion exchange, etc. However, the preferred procedure involves impregnation of the carrier material either before or after it is calcined and either before, during, or after the other components are added to the carrier material. Best results are ordinarily obtained when this component is added after the platinum, rhenium, and tin component because it serves to neutralize the acid used in the preferred impregnation procedure for incorporation of these components. Typically, the impregnation of the carrier material is performed by contacting same with a solution of a suitable decomposable compound or salt of the desired alkali or alkaline earth metal. Hence, suitable compounds include the halides, sulfates, nitrates, acetates, carbonates, phosphates, and the like compounds. For example, excellent results are obtained by impregnating the carrier material after the platinum group component, rhenium component, and tin component have been combined therewith with an aqueous solution of lithium nitrate or potassium nitrate. Following the impregnation step, the resulting'composite is dried and calcined in an air atmosphere as explained hereinafter.

Regardless of the details of how the components of the catalyst are composited with the alumina carrier material, the composite, after each of the components is added thereto, generally will be dried at a temperature of about 200 F. to about 600 F. for a period of from about 2 to 24 hours or more and finally calcined at a temperature of about 600 F. to about 1l0O F. in an air atmosphere for a period of about 0.5 to 10 hours, preferably about 1 to about 5 hours in order to substantially convert the metallic components to the oxide form. When acidic components are present in any of the reagents used to effect incorporation of any one of the components of the subject composite, it is a good practice to subject the resulting composite to a high temperature treatment with steam, either after or before the calcination step described above, in order to remove as much as possible of the undesired acidic component. For example, when the platinum group component is incorporated by impregnating the carrier material with chloroplatinic acid, it is preferred to subject the resulting composite to a high temperature treatment with steam in order to remove as much as possible of the undesired chloride.

-It is preferred that the resultant calcined catalytic composite be subjected to a substantially water-free reduction prior to its use in the conversion of hydrocarbons. This step is designed to insure a uniform and finely divided dispersion of the metallic components throughout the carrier material. Preferably, substantially pure and dry hydrogen (i.e., less than 20 vol. ppm. H is used as the reducing agent in this step. The reducing agent is contacted with the calcined composite at a temperature of about 800 F. to about 1200 F. and for a period of time of about 0.5 to hours or more, effective to substantially reduce the metallic components to their elemental state. This reduction treatment may be performed in situ as part of a start-up sequence if precautions are taken to predry the plant to a substantially water-free state and if sub stantially water-free hydrogen is used.

Although it is not essential, the resulting reduced catalytic composite may, in some cases, be beneficially subjected to a presulfiding operation designed to incorporate in the catalytic composite from about 0.05 to about 0.50 wt. percent sulfur calculated on an elemental basis. Preferably, this presulfiding treatment takes place in the presence of hydrogen and a suitable sulfur-containing compound such as hydrogen sulfide, lower molecular weight mercaptans, organic sulfides, etc. Typically, this procedure comprises treating the reduced catalyst with a sulfiding gas such as a mixture containing a mole ratio of H to 10 H S of about 10:1 at conditions sufiicient to effect the desired incorporation of sulfur, generally including a temperature ranging from about 50 F. up to about 1100 F. or more. This presulfiding step can be performed in situ or ex situ.

According to the method of the present invention, the dehydrogenatable hydrocarbon is contacted with a catalytic composite of the type described above in a dehydrogenation zone at dehydrogenation conditions. This contacting may be accomplished by using the catalyst in a fixed bed system, a moving bed system, a fluidized bed system, or in a batch type operation; however, in view of the danger of attrition losses of the valuable catalyst and of well known operational advantages, it is preferred to use a fixed bed system. In this system, the hydrocarbon feed stream is preheated by any suitable heating means to the desired reaction temperature and then passed into a dehydrogenation zone containing a fixed bed of the catalyst type previously characterized. It is, of course, understood that the dehydrogenation zone may be one or more separate reactors with suitable heating means therebetween to insure that the desired conversion temperature is maintained at the entrance to each reactor. It is also to be noted that the reactants may be contacted with the catalyst bed in either upward, downward, or radial flow fashion with the latter being preferred. In addition, it is to be noted that the reactants may be in the liquid phase, a mixed liquid-vapor phase, or vapor phase when they contact the catalyst, with best results obtained in the vapor phase.

Although hydrogen is the preferred diluent for use in the subject dehydrogenation method, in some cases other art-recognized diluents may be advantageously utilized such as steam, methane, carbon d oxide, and the like diluent. Hydrogen is preferred because it serves the dualfunction of not only lowering the partial pressure of the dehydrogenatable hydrocarbon, but also of suppressing the formation of hydrogen-deficient, carbonaceous deposits on the catalytic composite. Ordinarily, hydrogen is utilized in amounts sufficient to insure a hydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with best results obtained in the range of about 1.5:1 to about 10:1. The hydrogen stream charged to the dehydrogenation zone will typically be recycle hydrogen obtained from the etfiuent stream from this zone after a suitable separation step.

Regarding the conditions utilized in the process of the present invention, these are generally selected from the conditions well known to those skilled in the art for the particular dehydrogenatable hydrocarbon which is charged to the process. More specifically, suitable conversion temperatures are selected from the range of about 700 to about 1250 F., with a value being selected from the lower portion of this range for the more easily dehydrogenated hydrocarbons such as the long chain normal paraffins and from the higher portion of this range for the more difiicultly dehydrogenated hydrocarbons such as propane, butane, and the like hydrocarbons. For example, for the dehydrogenation of C to C normal paraffins, best results are ordinarily obtained at a temperature of about 800 to about 950 F. The pressure utilized is ordinarily selected at a value which is as low as possible consistent with the maintenance of catalyst stability and is usually about 0.1 to about 10 atmospheres with best results ordinarily obtained in the range of about .5 to about 3 atmospheres. In addition, a liquid hourly space velocity (calculated on the basis of the volume amount as a liquid or hydrocarbon changed to the dehydrogenation zone per hour divided by the volume of the catalyst bed utilized) is selected from the range of about 1 to about 40 hr." with best results for the dehydrogenation of long chain normal parafiins typically obtained at a relatively high space velocity of about 25 to 35 hr.

Regardless of the details concerning the operation of the dehydrogenation step, an effluent stream will be withdrawn therefrom. This efiluent will contain unconverted dehydrogenatable hydrocarbons, hydrogen, and products of the dehydrogenation reaction. This stream is typically cooled and passed to a separating zone wherein a hydrogen-rich vapor phase is allowed to separate from a hydrocarbon-rich liquid phase. In general, it is usually desired to recover the unreacted dehydrogenatable hydrocarbon from this hydrocarbon-rich liquid phase in order to make the dehydrogenation process economically attractive. This recovery can be accomplished in any suitable manner known to the art such as by passing the hydrocarbon-rich liquid phase through a bed of suitable adsorbent material which has the capability to selectively retain the dehydrogenated hydrocarbons contained therein or by contacting same with a solvent having a high selectivity for the dehydrogenated hydrocarbon, or by a suitable fractionation scheme where feasible. In the case where the dehydrogenated hydrocarbon is a mono-olefin, suitable adsorbents having this capability are activated silica gel, activated carbon, activated alumina, various types of specially prepared molecular sieves, and the like adsorbents. In another typical case, the dehydrogenated hydrocarbons can be separated from the unconverted dehydrogenatable hydrocarbons by utilizing the inherent capability of the dehydrogenated hydrocarbons to easily enter into several well known chemical reactions such as alkylation, oligomerization, halogenation, sulfonation, hydration, oxidation, and the like reactions. Irrespective of how the dehydrogenated hydrocarbons are separated from the unreacted hydrocarbons, a stream containing the unreacted dehydrogenatable hydrocarbons will typically be recovered from this hydrocarbon separation step and recycled to the dehydrogenation step. Likewise, the hydrogen phase present in the hydrogen separating zone W111 be withdrawn therefrom, a portion of it vented from the system in order to remove the net hydrogen make, and the remaining portion is typically recycled through suitable compressing means to the dehydrogenation step in order to provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chain normal paraifin hydrocarbons are dehydrogenated to the corresponding normal mono-olefins, a preferred mode of operation of this hydrocarbon step involves an alkylation reaction. In this mode, the hydrocanbon-rich liquid phase withdrawn from the separating zone is combined with a stream containing an alkylatable aromatic and the resulting mixture passed to an alkylation zone containing a suitable highly acid catalyst such as an anhydrous solution of hydrogen fluoride. In the alkylation zone the mono-olefins react with the alkylatable aromatic While the unconverted normal paraffins remain substantially unchanged. The efiluent stream from the alkylation zone can then be easily separated, typically by means of a suitable fractionation system, to allow recovery of the unreacted normal paraffins. The resulting stream of unconverted normal parafiins is then usually recycled, to the dehydrogenation step of the present invention.

The following working examples are introduced to illustrate further the novelty, mode of operation, utility, and benefits associated with the dehydrogenation method of the present invention. These examples are intended to be illustrative rather than restrictive.

These examples are all performed in a laboratory scale dehydrogenation plant comprising a reactor, a hydrogen separating zone, a heating means, cooling means, pumping means, compressing means, and the like equipment. In this plant, the feed stream containing the dehydrogenatable hydrocarbon is combined with a hydrogen stream and the resultant mixture heated to the desired conversion temperature, which refers herein to the temperature maintained at the inlet to the reactor. The heated mixture is then passed into contact with the catalyst which is maintained as a fixed bed of catalyst particles in the reactor. The pressures reported herein are recorded at the outlet from the reactor. An effluent stream is withdrawn from the reactor, cooled, and passed into the separating zone wherein a hydrogen gas phase separates from a hydrocarbon-rich liquid phase containing dehydrogenated hydrocarbons, unconverted dehydrogenatable hydrocarbons, and a minor amount of side products of the dehydrogenation reaction. A portion of the hydrogen-rich gas phase is recovered as excess recycle gas with the remaining portion being continuously recycled through suitable compressive means to the heating zone as described above. The hydrocarbon-rich liquid phase from the separating zone is withdrawn therefrom and subjected to analysis to determine conversion and selectivity for the desired dehydrogenated hydrocarbon as will be indicated in the examples. Conversion numbers of the dehydrogenatable hydrocarbon reported herein are all calculated on the basis of disappearance of the dehydrogenatable hydrocarbon and are expressed in mole percent. Similarly, selectivity numbers are reported on the basis of moles of desired hydrocarbon produced per moles of dehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these examples are prepared according to the following general method with suitable modifications in stoichiometry to achieve the compositions reported in each example. First, an alumina carrier material comprising A inch spheres is prepared by: forming an aluminum hydroxyl chloride sol by dissolving substantially pure aluminum pellets in a hydrochloric acid solution, adding hexamethylenetetramine to the sol, gelling the resulting solution by dropping it into an oil bath to form spherical particles of an alumina hydrogel, aging and washing the resulting particles with an ammoniacal solution and finally drying, calcining, and steaming the aged and washed particles to form spherical particles of gamma-alumina containing substantially less than 0.1 wt. percent combined chloride. Additional details as to this method of preparing this alumina carrier material are given in the teachings of US. Pat. No. 2,620,314. The resulting gamma-alumina particles are then contacted with an impregnation solution containing chloroplatinic acid, perrhenic acid, stannic chloride, and nitric acid in amounts sufiicient to yield a final catalytic composite containing the desired amounts of platinum, rhenium, and tin. The impregnated spheres are then dried at a temperature of about 300 F. for about an hour and thereafter calcined in an air atmosphere at a temperature of about 500 F. to about 1000 F. for about 2 to 10 hours. In general, it is a good practice to thereafter treat the resulting calcined particles with an air stream containing about 10 to about 30% steam at a temperature of about 1000" F. for an additional period of about 5 hours in order to further reduce the residual combined chloride contained in the catalyst. In the cases shown in the example where the catalyst utilized contains an alkali component, this component is added to the oxidized platinum, rhenium, and tin-containin g catalyst in a separate impregnation step. This second impregnation step involves contacting the oxidized particles with an aqueous solution of a suitable decomposable salt of the alkali component. For the catalyst utilized in the present examples, the salt is either lithium nitrate or potassium nitrate. The amount of the salt of the alkali metal utilized is chosen to result in a final catalyst of the desired composition. The resulting alkali impregnated particles are then dried and calcined in an air atmosphere in much the same manner as is described above following the first impregnation step.

In all of the examples the catalyst is reduced during start-up by contacting with hydrogen at an elevated temperature and thereafter sulfided with a mixture of H and Has.

EXAMPLE I The reactor is loaded with 100 cc. of a catalyst contaming, on an elemental basis, 0.75 wt. percent platinum,

0.5 wt. percent rhenium, 0.5 wt. percent tin, and less than 0.15 wt. percent chloride. The feed stream utilized is commercial grade isobutane containing 99.7 wt. percent isobutane and 0.3 Wt. percent normal butane. The feed stream is contacted with the catalyst at a temperature of 1065 F., a pressure of 10 p.s.i.g., a liquid hourly space velocity of 4.0 hr. and a hydrogen to hydrocarbon mole ratio of 2:1. The dehydrogenation plant is lined-out at these conditions and a 20 hour test period commenced. The hydrocarbon product stream from the plant is continuously analyzed by GLC (gas-liquid chromatography) and a high conversion of isobutane is observed with a selectivity for isobutylene of 80%.

EXAMPLE II The catalyst contains, on an elemental basis, 0.375 wt. percent platinum, 0.375 wt. percent rhenium, 0.5 wt. percent tin, 0.6 wt. percent lithium, and 0.15 Wt. percent combinedchloride. The feed stream is commercial grade normal dodecane. The dehydrogenation reactor is operated at a temperature of 870 F., a pressure of 10 p.s.i.g., a liquid hourly space velocity of 32 hl. and a hydrogen to hydrocarbon mole ratio of 8:1. After a line-out period a 20 hour test period is performed during which the average conversion of the normal dodecene is maintained at a high level with a selectivity for normal dodecene of about 90%.

EXAMPLE III The catalyst is the same as utilized in Example II. The feed stream is normal tetradodecane. The conditions utilized are a temperature of 840 F., a pressure of 20 p.s.i.g., a liquid hourly space velocity of 32 hrf and a hydrogen to hydrocarbon mole ratio of 8: 1. After a lineout period, a 20 hour test shows an average conversion of about 12.0%, and a selectivity for normal tetradodecene of 90%.

EXAMPLE IV The catalyst contains, on an elemental basis, 0.30 wt. percent platinum, 0.30 wt. percent rhenium, 1.0 wt. percent tin, and 0.6 wt. percent lithium, with combined chloride being less than 0.2 wt. percent. The feed stream is substantially pure normal butane. The conditions utilized are a temperature of 950 F., a pressure of 15 p.s.i.g., a liquid hourly space velocity of 4.0 hr.- and a hydrogen to hydrocarbon mole ratio of 4: 1. After a line-out period, a 20 hour test is performed with the average conversion of the normal butane being about 30% and the selectivity for normal butane is about 80%.

14 EXAMPLE V The catalyst contains, on an elemental basis, 0.75 wt. percent platinum, 0.5 wt. percent rhenium, 1.0 wt. percent tin, 1.5 wt. percent potassium, and less than 0.2 wt. percent combined chloride. The feed stream is commercial grade ethylbenzene. The conditions utilized are a pressure of 15 p.s.i.g., a liquid hourly space velocity of 32 hrf a temperature of 1050 F., and a hydrogen to hydrocarbon mole ratio of 8:1. During a 20 hour test period, of equilibrium conversion of the ethylbenzene is observed. The selectivity for styrene is 98.0%.

I claim as my invention:

1. A catalytic composite comprising a combination of a platinum group component, a rhenium component, a tin component, and an alkali or alkaline earth component with a porous carrier material wherein the components are present in amounts sufiicient to result in the composite containing, on an elemental basis, about 0.01 to about 1 wt. percent platinum group metal, about 0.01 to about 1 wt. percent rhenium, about 0.01 to about 5 wt. percent tin, and about 0.01 to about 5 wt. percent of the alkali metal or alkaline earth metal.

2. A catalytic composite as defined in claim 1 wherein the platinum group component is platinum or a compound of platinum.

3. A catalytic composite as defined in claim 1 wherein said porous carrier material is a refractory inorganic oxide.

4. A catalytic composite as defined in claim 3 wherein said refractory inorganic oxide is alumina.

5. A catalytic composite as defined in claim 1 wherein said alkali metal component is a compound of potassium.

6. A catalytic composite as defined in claim 1 wherein said alkali metal component is a compound of lithium,

References Cited UNITED STATES PATENTS 3,326,961 6/1967 Eden et a1 252439X 3,389,965 6/ 1968 Ruiter et a1. 252439X 3,449,078 6/ 1969 Quik et a1. 252466X 3,449,237 6/ 1969 Jacobson et al. 252466X CURTIS R. DAVIS, Primary Examiner US. Cl. X.R. 

